1. Field of the Invention
The present invention relates generally to pulsation dampeners and, more particularly, pulsation dampening devices which permit adequate purging of bubbles in photographic film and paper coating operations.
2. Brief Description of the Prior Art
In the production of photographic film various coatings are delivered to traveling base webs such as, for example, polyethylene terephthalate and acetate. These coatings often include aqueous solutions of gelatin in which light-sensitive substances have been dispersed. It is important that these coatings be applied evenly to the traveling base web. This is typically done by causing the base web to travel through a coating apparatus such as, for example, a curtain coating apparatus or a bead coating apparatus. It is important to ensure that a stable laminar flow of coating solution is formed by the slide hopper of the coating apparatus. Therefore, pulsation dampening devices are often used in the conduits supplying the coating solution to the coating apparatus.
Numerous devices for pulsation dampening are known in the prior art. Most of such devices are addressed to large pulsations associated with water hammering and shock systems. For example, U.S. Pat. No. 3,628,573 to Lolliger teaches a diaphragm chamber-dampening device with a dished shell for dampening fluid shocks in pipe systems, particularly in the sterilizable pipe systems.
U.S. Pat. No. 4,548,240 to Graham teaches a hydraulic pulse dampener for use in high pressure environments of liquid chromatographs which includes a stiff diaphragm adjacent a recess formed in a receiving member. When the diaphragm is flexed due to absolute increases in pressure or to pressure pulses in the liquid, the diaphragm is capable of nesting in the receiving member.
U.S. Pat. No. 4,222,414 to Achener teaches yet another pulse dampener for use in high pressure liquid pumping applications such as liquid chromatography. The pulse damper includes plastic spools which reside within a housing. Contained within the housing and surrounding the spool is a cavity which can be filled with a compressible liquid.
U.S. Pat. No. 4,186,775 to Muroi teaches a water hammer shock absorber including a housing having a cavity therein adapted to have a pressurized gas seal therein, a perforated pipe passes through the housing with an elastic tube covering the perforated pipe. When there is an occurrence of water hammer within the fluid piping, the pressure waves affected thereby run out through the small perforations in the perforated pipe thereby temporarily deforming the elastic tube. Apparently, the pressure waves are absorbed by means of balancing the force of the pressure waves with the sum of the elasticity of the plastic tube and the pressure to the outside of the elastic tube affected by the pressurized gas within the cavity.
The pulsation dampeners of the prior art are generally vertically oriented meaning that the longitudinal or cylindrical axis of the fluid chamber is vertically oriented and the diaphragm resides in a horizontal plane. It is known that such vertically oriented pulsation dampeners have included multiple air chambers on the opposite side of the diaphragm from the fluid chamber.
Nothing in the prior art teaches a pulsation dampening device which is designed to allow for effective purging in order to deliver bubble free fluid from the device. For film sensitizing applications the ability to purge the dampening device is critical as bubbles delivered in the coating operation result in physical defects in the end product which can make the end product unsuitable for use.